There is a long-felt need for low-friction rotating devices that require no or little lubrication. Since the first wheel, there has been a compelling need for reliable and low friction rotating bearings and other rotary devices. Prior rotary devices inherently produce friction as they convert one form of motion, e.g., rotation, into another form of motion, e.g., linear movement, or energy. Prior rotary devices, such as roller bearings, require lubrication to reduce friction and are prone to failure if not properly lubricated and maintained. In these prior devices, friction between two surfaces, such as a bearing surface and a roller bearing, degrade the efficiency of the device, and produce undesirable heat and wear that can damage the rolling surfaces, break down needed lubrication and reduce the useful life of the device. The lubrication required for most prior art rotary devices reduces the operating efficiency of the devices; must be filtered, replaced or shielded; limits the operating environment to conditions favorable to lubrication; traps dirt and grit, and necessitates seals and dust covers to protect the lubrication. In addition, these seals and dust covers contribute to friction losses. Furthermore, prior art rotary devices generally are manufactured to narrow tolerances that necessitate high degrees of manufacturing accuracy that make the manufacture of such devices expensive and difficult. The difficulties caused by high friction, lubrication and narrow manufacturing tolerances have plagued prior art rotary devices.
The lubricants needed for prior rotary devices degrade, trap particles between rotating surfaces and perform poorly in extreme conditions. Prior rotary devices are susceptible to dirt, grit and other debris suspended in the lubricant. Debris and grit caught between the contacting surfaces in a conventional rotary device tends to gouge surfaces and cause seizure of the rotating elements of the device. Similarly, extreme operating conditions, such as under water, weather exposure, in fire, dust and dirt and in outer space, generally render most conventional lubricants useless as such lubricants are not suitable for these extreme conditions. In addition, lubricants tend to degrade, evaporate or slide off surfaces during long term storage of rotary devices. Furthermore, rotary devices are not readily micro-miniaturized because of the difficulty in lubricating micro-machined components and because lubricants are generally not suitable for micro-miniaturized devices. In addition, friction--and the lack of accuracy in micro-manufacture techniques--pose problems that are difficult to overcome in the micro-miniaturization of rotary devices. Accordingly, extreme conditions, long term storage and micro-miniaturization are examples of circumstances where conventional rotary devices have failed to perform as needed.
Nearly twenty years ago, an oscillating (non-rotary) roller band device was invented by Donald F. Wilkes at Sandia Laboratories that came to be known as a "rolamite" device. This rolamite device is described in U.S. Pat. No. 3,452,175, entitled "Roller Band Device," that issued Jun. 24, 1969. The rolamite device included a guide housing having two or more rollers and an S-shaped flexible band that looped around each roller. The band and the housing constrained the movement of the rolling shafts to effect the desired oscillating movement. Mr. Wilkes further described his roller band device in a report entitled "Rolamite: A New Mechanical Design Concept" (Research Report SC-RR-67-656A) printed in December 1967 by Sandia Laboratories. This report describes several embodiments of the roller band device.
Mr. Wilkes received substantial publicity for his roller band device in the late 1960's. Several articles on roller band devices were published in popular technical journals that heralded Mr. Wilkes and his invention. Indeed, one of these articles reported that the rolamite device was the twenty-sixth fundamental mechanism of all time and the first fundamentally new fundamental mechanism since the clutch invented before 1814. See "Popular Mechanics," p. 95 (February 1968).
The roller band device developed by Mr. Wilkes has never achieved wide-spread commercial use. There are limited applications of roller band devices in weapons and crash sensors where oscillating movement is required. But, these applications of oscillating devices do not represent the wide use enjoyed by roller-bearings and other every day rotary devices. A fundamental limiting feature of the rolamite device is that it provides oscillation, but does not effectively provide rotation. A large portion of all mechanical devices rely on rotation to transfer energy and motion. Indeed, roller bearings, cams, gears and many other common devices apply rotation.
Despite several prior attempts over 27-years to develop effective and practical rotary roller band devices, no practical rotary roller band device was developed, until the present invention. In this regard, Mr. Wilkes wrote that "only a few rotary rolamite devices have been modeled. Most of these models exhibited good oscillatory performance, but with all of them continuous rotation resulted in band failure." D. F. Wilkes, "Rolamite: A New Mechanical Design Concept", Research Report SC-RR-67-656A, p. 179 (Sandia Labs. December 1967). It is believed that prior rotary roller band devices failed principally due to band failure caused by rubbing between adjacent bands, and to unwanted sliding between the bands and band guideways resulting from inadequate contact between the bands and guideways.
Of the many other patents that have issued on roller band devices, only U.S. Pat. No. 3,691,871 issued to Dean Gladow et al. in 1972 was found that discloses a rotary motion roller band device. The Gladow patent discloses a complicated arrangement of rollers having a central roller and three orbiting roller pairs. The. roller pairs orbit the central roller and ride against an annular guide surface. A roller band holds these three layers of rollers together. The rotary device disclosed in the Gladow patent is believed to have inadequate stability of the orbiting roller pairs and insufficient contact between the orbiting roller pairs and outer annular guide surface. Accordingly, there has been a long-felt need in the art for a rotary roller band device and several technical failures to achieve such a device.
The present invention is a novel and unobvious rotary roller band device that solves the prior problems of band failure of prior rotary roller band devices. The invention provides rotary motion with minimal friction and slippage between bands and rollers. Whereas prior roller band devices require three elemental components (rollers, bands and housing), the current invention has just two elemental components which are rollers and bands. With just two components, the invention is self-supporting and does not require a housing to hold the rollers and bands together as do prior roller band devices. The current invention embodies a new mechanical geometry previously unknown that is elegant in the simplicity of just two elemental components. The unique geometry of the invention is inherently stable in that its novel combination of rollers and bands is self-supporting and self-aligning, and employs unique geometric methods of operation in the manner that the bands weave through the rollers during rotation.
In particular, the current invention in one embodiment is a central roller concentric to an array cluster of outer counter-rollers that freely rotate about the central roller. The rollers are interconnected by bands that weave around the central roller and outer orbiting rollers. The bands are flexible and hold the rollers snugly in parallel and constrain the rolling movement of the rollers such that the outer rollers orbit the central roller. As the rollers rotate, the bands move in endless loops between and around the rollers. The surfaces of the bands are in a low-friction rolling engagement with the rotating surfaces of the rollers.
A particularly novel feature of the invention is that the bands are arranged such that the outer orbiting rollers are disposed within the loops of the roller bands and roll against the inside surface of the bands. The central roller is disposed outside of the loops formed by the bands and the central roller rolls against the outside surface of the bands. The band loops are each held in a C-shape where the cup (inside) of the "C" receives the central roller in a self-supporting nesting arrangement. Accordingly, the band wraps around most but not all of the circumference of the central roller and, thus, the band has virtually slip-free contact with the surface of the central roller.
The orbiting outer rollers are inside the loops of the roller bands. Of the orbiting outer rollers in the C-shaped loop, two adjacent outer rollers form the ends of the "C". The band curves around more that one-half of the circumference of each of these two outer rollers. Because the band wraps tautly around these two outer rollers at the ends of the "C", these outer rollers are held securely by the bands at these taut loop ends. At least one band wraps around each of the orbiting rollers because the orientation of the C-shaped loop of the different bands is shifted (off set) from band to band. In this manner, the orbiting rollers are held parallel to the central roller because of the support imparted by at least one band that wraps without slippage around more than one-half of the circumference of the roller in a row. Moreover, the outer rollers are also forced inward towards the central roller by the bands that pass over the outer roller, but do not wrap around the roller as happens to the rollers at the ends of the "C" of the roller band loops.
It is an object of this invention to provide a rotary mechanical device having low-friction rolling contact between elements in contact, and that avoids high-friction rubbing and sliding contact between elements. It is another object of this invention to provide rotating mechanical devices that have relatively low coefficients of friction and do not require lubricants.
Another object of this invention is to provide a mechanism that is extremely tolerant of surface irregularities and imperfections. The rotating members and bands readily roll over small foreign particles, such as dust or grit, without jamming and can tolerate deforming pressures on rotating load bearing surfaces of the rotary device.
In addition, the invention provides inherent directional insensitivity, e.g., remains in balanced self-alignment, along the longitudinal axis of the rotary motion. In this regard, the invention is insensitive to extraneous side loads and other forces because the forces between the bands and rolling members counteract and balance the extraneous side loads. Similarly, the geometry of the invention inherently provides good side load bearing capability as the side load components act parallel to the roller axes and, thus, can be borne without increasing friction in the device. Moreover, abnormally high forces, side loads and torques of unpredictable, infrequent or sporadic nature can be borne by the invention due to the balanced forces acting on the flexible bands and rollers, and between rollers. Accordingly, the invention is well suited to heavy load bearing applications.
A further object of this invention is to provide a device wherein the costs of manufacturing are minimal as compared to the costs of manufacturing other rotary devices. The device is extremely tolerant to minor imperfections in its own geometry and, thus, allows for wide tolerances in production controls and in minor dimensional aberrations and inaccuracies. Because the invention allows for wide tolerances in manufacture, its manufacturing cost should be significantly lower than the costs of manufacturing precision bearings. Furthermore, the large tolerances offered by the invention are helpful for micro-miniaturized devices. In addition, the invention may be constructed of standardized modular parts that can be easily configured to various applications. Indeed, the modularity of the invention provides a wide range of functional results with only minor variations in construction, allowing for time and cost savings, adaptive manufacturing methods in which the tooling for a single assembly line can be readily modified during production to adapt to different manufacturing or product requirements. Minor modular modifications in the invention can yield products having major functional differences.
In one embodiment, the invention is a rotary roller band device that comprises a central rotating element and a plurality of orbiting rotating elements concentrically arranged around the central rotating element. A row of bands is intertwined between the rotating elements, each band is held in a C-shaped loop disposed partially around each of the rotating elements, the bands are flexible and held taut by the rotating elements, and the bands hold the elements in parallel. The orbiting elements rotate counter to the central rotating element, and the elements roll within the bands which move in endless loops.
In another embodiment the invention is a rotary device comprising a central roller, at least three outer rollers orbiting and concentric to the central roller, and a plurality of bands in a row each forming a loop having an inside surface and an outer surface. Each of the bands are disposed around the central roller such that the outer surface of the band loop is in rolling contact with the central roller, and the outer rollers are disposed in the band loop such that the outer rollers are in rolling contact with the inside surface of the loop.
The invention also comprises a method for creating low friction rotational motion with a rotary device having a central element, orbiting elements and roller bands that includes the steps of: positioning a plurality of orbiting rotating elements concentrically around a central element; weaving a row of roller bands between the rotating elements, holding each band in a C-shaped loop disposed partially around each of the rotating elements wherein each loop is offset with respect to other loops, and wherein the bands are flexible and provide stable support to the rotating elements; holding the orbiting elements parallel to the central element with the bands, and rotating the orbiting elements counter to the rotation of the central element and rotating the elements with the bands that move in endless loops.
These objects, and others, are attained by the invention described in a preferred embodiment below.